1. Field of the Invention
The present invention relates generally to integrated circuits and, more particularly, to pressure transducer structures and efficient methods for fabricating the same.
2. Description of the Related Art
Pressure transducers are devices that are typically fabricated into semiconductor devices to sense external pressure conditions. In some applications, pressure transducers are coupled to integrated control circuitry that may be triggered to perform an operation in response to the sensed external pressures.
For ease of understanding, FIG. 1A shows a cross-sectional view of a pressure transducer structure 100. The pressure transducer structure 100 is fabricated over a substrate 102. The substrate 102 has an inter-metal oxide 104 formed thereon, and a patterned metallization layer 108 formed over the inter-metal oxide 104. An inter-metal oxide 106 is then formed over the patterned metallization layer 108 and portions of the inter-metal oxide layer 104. During the fabrication process, a hole 114 is etched into the inter-metal oxide layer 106 to define a cavity having a bottom surface that is the patterned metallization layer 108.
Once the hole 114 is defined, a sacrificial oxide material is deposited into the hole 114 before a patterned metallization layer 110 is formed over the inter-metal oxide layer 106. Conventionally, the sacrificial oxide material is deposited into the hole 114 to provide mechanical support for the subsequently formed patterned metallization layer 110. However, the sacrificial oxide material must be removed from the hole 114 before an oxide layer 112 is deposited over the inter-metal oxide layer 106 and the patterned metallization layer 110.
As shown in FIG. 1B, a portion of the hole 114 is left exposed once the patterned metallization layer 110 is formed over the inter-metal oxide layer 106 to enable a wet etch chemical to come into contact with the sacrificial oxide (i.e., that is contained in the hole 114). Once all of the sacrificial oxide is removed from the hole 114, the oxide layer 112 is deposited over the inter-metal oxide layer 106 and the patterned metallization layer 110. At this point, the pressure transducer structure 100 is complete, and a voltage may be measured between the patterned metallization layer 108 and the patterned metallization layer 110 to determine an external pressure.
In this example, a pressure P.sub.1 is shown applied to the oxide layer 112 that lies over the hole 114. In pressure transducers, the pressure P.sub.1 may be determined by measuring the capacitance C.sub.1 detected between the patterned metallization layers 108 and 110. When the pressure increases by .DELTA.P as shown in FIG. 1C, the patterned metallization layer 110 and the oxide layer 112 will compress into the hole 114. When this happens, the capacitance C.sub.1 of FIG. 1A will change to a capacitance C.sub.2, which is measured between the patterned metallization layers 108 and 110. By measuring the new capacitance value, it is possible to accurately determine the new increased external pressure.
Although these conventional pressure transducer structures 100 find many practical applications in devices, such as, altitude sensors, flow meters, accelerometers for deploying airbags in automobiles, and other useful applications, they unfortunately add substantial manufacturing complexities to standard CMOS circuitry manufacturing.
Thus, in order to manufacture conventional pressure transducers, an additional level of manufacturing must be completed after the interconnecting contact structures are formed. For example, once the interconnecting structures are formed, an additional application of photoresist must be applied and patterned to define the location of the hole for the pressure transducer. Once the photoresist mask is formed, the pressure transducer hole is etched and filled with the sacrificial oxide. Next, the excess sacrificial oxide may be removed with a chemical mechanical polishing operation before the patterned metallization layer 110 is applied. Next, the sacrificial oxide is removed with the wet etching process before the oxide layer 112 is applied. As can be appreciated, the process of integrating pressure transducers into standard CMOS circuitry manufacturing is a task that increases complexity and adds a substantial amount of cost to CMOS fabrication operations.
In view of the foregoing, there is a need for a method and apparatus for manufacturing integrated circuit devices that include pressure transducer structures, without increasing manufacturing complexity.